Flash Synchronization - Wireless Sync

Wireless Sync

Some synchronization methods employ optical or radio triggering that requires no electrical connection to the camera or main flash unit. This allows the camera to move without the restriction of cables. Optical triggering requires at least one flash electrically connected to the camera. A sensor, either built-in or external to a remote slave flash unit, will sense the light from the master flash and cause a remote flash to fire. Radio triggering requires a transmitter electrically connected to the camera to trigger a remote receiver connected to (or embedded into) a remote flash unit.

One of the problems with optical triggering is that in modern digital cameras a built-in or shoemount flash releases one or more 'pre-flashes'. Many optical slave units will respond to the pre-flash, thus firing the slave flash too early. Sometimes this can be prevented by setting the camera to manual ('M'). However, a good number of cameras will still fire pre-flashes even on a manual setting. This is equally true for compact cameras as well as the more professional digital SLR cameras. Still, a flash connected to the PC jack on a camera or in the hotshoe will usually not fire pre-flashes in the 'M' setting and therefore can be used to optically trigger a number of slave flashes.

Many compact cameras, however, only have a built-in flash and no hotshoe and no connector for an external flash and there is no way to suppress the pre-flash. In those instances, slave units are used that are able to skip a number of flashes, thus skipping one or more pre-flashes and only firing simultaneously with the main flash firing. Some modern flash units have this capacity built in. An example at the low end is the Godox 18, a simple flash unit that can be set to skip a max of 3 flashes. A more advanced flash that can set to skip one pre-flash is the popular 'strobist' flash, the Lumopro160. Also, some studio flashes can be set to ignore pre-flash.

Rather than selecting a specific number of pre-flashes to ignore, some slave units have a learning mode in which firing one flash teaches them on which flash to synchronise.

Several camera equipment manufacturers have support for remote flash triggering built into at least some of their camera and flash models. This eliminates the issue of slave flashes triggering upon seeing a pre-flash, as the master flash unit (whether a shoemount flash or the camera's pop-up flash) sends predefined signals to the slave units to control them. However, the user is restricted to using flash units from that camera manufacturer, or a limited selection of third-party units which are compatible with it.